It is known for a film cartridge to have a film exposure status indicator for providing a visual indication of whether a filmstrip inside the cartridge housing has been exposed. Such indication is useful, for example, when a roll of film is exposed in a camera over several frames and then is partially rewound. When removed from a camera, such a roll may have the appearance of a completely unexposed roll, which can lead to inadvertent double exposure of frames and significant loss and inconvenience to the photographer.
Indication of exposure is readily achieved by indicating the direction of any rotation of a film spool subsequent to its assembly into a film cartridge. Such indication may take the form, for example, of changing the visual status of an indicator window when the spool completes at least one full revolution in the unwinding direction. This indication suffers in that simply loading a cartridge into a camera may require that sufficient film is pulled out of the cartridge to trip the exposed indicator. If the cartridge is then removed from the camera without being used, the indication of film exposure is erroneous. An alternative, and superior, strategy is to indicate that film has been exposed only when the spool has been rotated some amount in the rewind direction.
Prior art U.S. Pat. No. 5,278,600, issued Jan. 11, 1994, discloses a film cartridge comprising a film spool rotatable inside the cartridge housing, an indicator window in an end cap of the cartridge housing, an annular indicator wheel rotatable inside the cartridge housing behind the indicator window to move a film-exposed indication on the indicator wheel to the indication window, and an annular drive wheel rotatably linked with the film spool for rotating the indicator wheel to move the film-exposed indication to the indication window. A pin and receiver clutch device transmits movement of the drive wheel to the indicator wheel when the film spool is rotated in a film unwinding direction, and leaves the indicator wheel and the drive wheel disconnected when the film spool is rotated in a film rewinding direction. This apparatus has the double disadvantage of requiring a redesigned cartridge and of indicating exposure by spool rotation in the unwind direction.
Some other disclosures of exposure status indicators are found in U.S. Pat. Nos. 4,978,985, issued Dec. 18, 1990; 5,153,627, issued Oct. 6, 1992; 5,475,454, issued Dec. 12, 1995; and EPO Patent No. EP 0 431 529 B1, filed on Mar. 12, 1990. Each of these disclosed indicators requires at least a significant modification of the shell or end caps of a standard 35 mm film cartridge to provide an indicator window. In some cases, an entirely redesigned cartridge is required. None of them is useful in conjunction with a standard cartridge having no modification to its shell or end caps.
Thus a need exists for a film exposure status indicator which can be added to an unmodified cartridge or which requires modification of only the film spool and not of the cartridge shell or end caps, and which preferably can be constructed alternatively to be operable in the unwind or rewind direction, as desired by the manufacturer.
A further need exists for such an indicator which can be easily added to a standard film cartridge in a spooling and assembly line.
A further need exists for such an indicator which can be preassembled to a partially-formed cartridge in white lights prior to spooling and installation of a filmstrip into the cartridge in the dark, and particularly which can be preassembled as a self-contained film exposure status indicator module.